1. Field of the Invention
The present invention relates to a projection optical system, and more particularly to a projection optical system having a wedge prism for light collection efficiency.
2. Description of the Related Art
As shown in FIG. 1, a light source module 1, a color wheel 3, an integration rod 4, and a relay lens 5 are coaxial in a prior art non-telecentric projection optical system, but a light valve 6 and a projection lens 7 aren't coaxial with the above-mentioned devices. As the light source module 1 producing a illuminating light beam, travels through the color wheel 3, the integration rod 4, and the relay lens 5 into a reflection mirror 8. The reflection mirror 8 reflects the light beam obliquely into the light valve 6. After dealt by the light valve 6, the images through the projection lens are finally formed on the projection screen 9.
Because of the reflection illuminating light beam's oblique incidence on the light valve 6, the reflection optical paths from the reflection mirror 8 to each pixel on the light valve 6 do not extend over the same distance. As shown in FIG. 2, the reflection illuminating light beam should have the same optical path and focus on focuses Fa, Fb, and Fc, but because of the different optical path lengths, only the central focus Fb can focus on the right position. The focuses fa and Fc can't certainly focus and cause the defocus phenomenon. As a result, the illuminating light beam can't certainly focus on the light valve 6 and cause the illuminating area on the plane of the light valve 6 to increase. As shown in FIG. 3, the light spot (shown in A, B) on the same plane of the light valve 6 is deformed, and forms lower and non-uniform brightness, affecting the collection efficiency of the light valve 6.